The invention relates to a method and an apparatus for electronically controlling a throttle valve by a motor and, more particularly, to control method and apparatus of a throttle valve for feedback controlling a position of the throttle valve.
In position control of an electronic controlled throttle, a technique for improving position resolution of a throttle valve has conventionally been used in order to control an idling rotational speed so as to become a constant speed. According to the position control, a position of the throttle valve detected by a sensor is converted into a digital value by an A/D converter constructed by a microcomputer, and a motor is controlled by software by using PID control or the like so that an opening degree of the throttle valve coincides with a target value on the basis of a difference (hereinafter, referred to as a deviation) between the actual position and the target position of the throttle valve.
Therefore, if the user tries to finely move the throttle valve by 0.1 degree or the like, not only an influence of friction which is caused in rotary axes of the motor, a gear, and the valve but also an influence of friction of a brush in case of using a DC motor as a motor cannot be ignored. It takes a longer time until the opening degree of the throttle valve coincides with the target value than that in the case where the target position changes largely by tens of degrees or the like.
Therefore, in JP-A-10-47135 and JP-A-7-332136, there has been disclosed the technique such that the smaller the deviation between the position of the throttle valve and the target position is, the more a gain of the PID control is increased, or in the Official Gazette of international publication WO99/53182, there has been disclosed the technique of switching to a large correction coefficient at the time of micro opening degree control.
Further, in JP-A-10-238370 and JP-A-2001-73817, there has been disclosed the method whereby an integration term is controlled to a specific value (including a removal of the integration term) at a position near a switching position of action forces of a return spring and a default spring (a spring for limp-home condition of a vehicle) which act on the throttle valve.
Since resolution of the general A/D converter built in the microcomputer is up to 10 bits, an angle from a full closing state to a full open state of the valve is equal to about 90 degrees. Therefore, in case of performing the A/D conversion by 10 bits, the resolution of the position detection is equal to about 0.1 degree, and it is impossible to control at a precision of 0.1 degree. Therefore, in order to improve the resolution of the position detection only for a limited area near 10 degrees from the full closing state where control resolution corresponds to necessary idling rotational speed control, an output of the position sensor is transmitted through an amplifier of, for example, 4 times and A/D converted, thereby raising the resolution by two bits (refer to JP-A-6-101550).
A method of improving the resolution of the position detection by using a process after the A/D conversion by oversampling is also used.